Amine functional polymers are of growing commercial interest because of their versatility in being tailored for specific uses. The amine functionality of these polymers enables them to interact chemically so as to enhance their performance in certain applications. For example, amine functional polymers have been found useful as crosslinking agents for epoxy resins and polyurethanes, in enhanced oil recovery, as flocculants in processes such as wastewater treatment, and in papermaking as wet-end additives to improve paper wet strength.
It is known that the amine functionality in polymers can react with epoxy compositions in a curing process. U.S. Pat. Nos. 4,238,579, Leonard, Jr. et al. (1980) and 4,260,714, Wingard, Jr. et al. (1981) disclose that certain vinylamine copolymers can be used to cure epoxy resins in the manufacture of adhesives, potting resins, self-supporting reinforced composites and the like. Also, U.S. Pat. No. 4,778,725, Serizawa et al. (1988) describes making polymers having side chains containing terminal allyl groups by reacting a poly(vinylamine) with an allyl compound containing an epoxy group. The purpose of adding these side chains is to use the crosslinking properties of these unsaturated groups in the formation of self-supporting films and coated substrates. Ikemura, Kobunshi Kagaku, 26(288), pp 306-10 (1969) describes synthesizing polymers by graft copolymerization of ethylene oxide or propylene oxide onto poly(vinylamine). The result is said to be increased water solubility of the poly(vinylamine).
One of the more promising markets for vinylamine polymers takes advantage of the flocculating properties of these materials in operatons which require separation of water from suspended solids. Use of high molecular weight poly(vinylamine hydrochloride) as a flocculating agent is disclosed by U.S. Pat. No. 4,217,214, Dubin (1980). U.S. Pat. No. 4,421,602, Brunnmueller, et al. (1983) describes partially hydrolyzed homopolymers of N-vinylformamide as being useful as retention agents, drainage aids and flocculants in papermaking. European Patent Application 0,331,047 (1989) notes the utility of high molecular weight poly(vinylamine) as a wet-end additive in papermaking for improving dry strength of the product and as a filler retention aid.
U.S. Pat. No. 4,952,656, Lai et al. (1990) describes high molecular weight vinylamine homopolymers which can be made by inverse emulsion polymerization of N-vinylamides such as N-vinylformamide. Use as wet-end papermaking additives is among several utilities mentioned. Also, U.S. Pat. No. 4,978,427, Pfohl et al. (1990) discloses hydrolyzed copolymers of N-vinylformamide and ethylenically unsaturated monomers, such as vinyl acetate, which can be used in papermaking to increase product wet strength by addition of the copolymer to the pulp stock suspension in amounts of 0.1 to 5 weight percent based upon the dry fiber.
Market demand for tailored additives has stimulated further interest im modification of vinylamine polymers to increase their usefulness in specific applications. This has been done to increase their hydrophobic character, for example, by reaction with monoaldehydes. U.S. Pat. No. 5,086,111, Pinschmidt, Jr., et al. (1992) describes polyvinyl acetals containing amine functionality made by reacting a monoaldehyde and a poly(vinylamine) which includes both vinylamine homopolymers and copolymers containing ester and/or hydroxy groups. Such poly(vinylamines) have weight average molecular weights from 10,000 to 7 million. These polyvinyl acetals are shown to be useful as floculating agents.
It remains highly desirable to find ways to modify vinylamine polymers in order to change their hydrophobic character or alter other properties to increase their effectiveness in specific applications. One such application is in the retention of fines in papermaking processes. This is particularly a problem when dealing with recycled pulps because of the higher fines levels. Loss of fines during dewatering typically results in poorer physical properties of the finished product as well as reducing yield. This also causes higher fines levels in the processing water leading to costlier and more frequent clean-up.
At present, several types of polymers are being used in various ways to improve fines retention in papermaking. Polymer types used include cationic polymers such as copolymers of acrylamides and quaternary amines, anionic polymers such as copolymers of acrylamide and acrylic acid, and amphoteric polymers such as a polymer of a quaternary amine and acrylic acid. A common method for retaining these fine particles is first to add alum which negates the repulsive forces between the negatively charged cellulosic surface of the fiber and the negatively charged filler particles. Then a cationic polymer is added which bridges the two types of anionic surfaces and binds them together. Several newer systems now being used in this service include blends of cationic polyacrylamides with anionic fillers such as kaolin clays. Another type of blend is a cationic starch with anionic colloidal silica. Despite the wide variety of retention aids available, there continues to be a need for even better fines retention agents as the use of recycled papers continues to grow.